The length needed to cut is 91 x 23mm, you will need to file off the lip on the lid on the mounting side to get this to close proper. It has to be done this way as the chip is wide and you want an insert that wont fall apart on you.

After building several SX350 mods the only thing I would say is missing are mounting holes. You will need to either epoxy or hot glue the chip and charger in.